1. Field of the Invention
This invention relates to resin impregnated porous sheet materials, and more particularly, to resin impregnated fibrous webs having a uniform density throughout which can be further processed into simulated leather-like sheet materials.
2. Description of the Prior Art
Resin impregnated porous sheet materials such as cloth, batts, waterleaves and the like are well known in the art. These resin impregnated sheet materials are useful for a plurality of purposes, including imitation leather in the form of vinyls and the like, structural sheet materials such as conveyor belts, and similar products.
Prior art methods of impregnating a particular web involve the impregnation or coating of a porous material with a polymeric resin such as a polyurethane, vinyl or a similar material. Polyurethanes have met with wide acceptance as a coating or impregnating composition due to their capability of wide variation in chemical and physical properties, particularly their flexibility and chemical resistance. In impregnating the porous sheet material with a polymeric resin, several techniques have been employed. One such prior art method involves the use of the polymeric resin in an organic solvent system wherein the sheet material is dipped in the solution and the solvent is removed therefrom. These solvent systems are undesirable since the solvent, in many cases, is toxic and must either be recovered for reuse or discarded. These solvent systems are expensive and do not necessarily provide a desirable product since upon evaporation of the solvent from the impregnated porous sheet material, the resin tends to migrate to provide a non-homogeneous impregnation of the porous sheet material, resulting in resin richness toward the surface of the sheet material rather than uniform impregnation. In order to alleviate the problems with solvent systems, certain aqueous polymeric systems have been proposed. In forming impregnated sheet materials by impregnation with aqueous polymers, the aqueous portion must be removed. Again, heat is required and migration of the polymer to the surfaces of the impregnated sheet material is encountered.
In one method of combining polyurethane solutions with porous substrates, the polymer is applied in an organic solvent to a substrate, such as a needle punched polyester batt. The polymer-substrate composite is subsequently bathed with a mixture of organic solvent for the polymer and a non-solvent for the polymer that is at least partially miscible with the solvent until the layer is coagulated into a cellular structure of interconnected micropores. The solvent is removed from the coating layer along with the non-solvent to produce a solvent-free microporous layer. Although this process yields acceptable properties for a polyurethane impregnated fabric, it has the disadvantage of an organic solvent system, particularly when high performance polyurethanes are utilized which require relatively toxic and high boiling solvents. An example of this method is disclosed in U.S. Pat. No. 3,208,875.
In another method, polyurethane dispersions in organic vehicles have been proposed and used to coat porous substrates such as is disclosed in U.S. Pat. No. 3,100,721. In this system, a dispersion is applied to a substrate, and coagulated by further addition of a non-solvent. Although this approach has been used with some success, it involves two major limitations: (1) the vehicle of the dispersion is substantially organic since relatively small amounts of non-solvent, preferably water, are needed to form a dispersion; and (2) there is a narrow useful range of added non-solvent so that reproducible results are difficult to obtain.
One particularly useful method of preparing composite sheet material by impregnating a porous substrate is disclosed in U.S. Pat. No. 4,171,391, incorporated herein by reference. In this system, a porous sheet material is impregnated with an aqueous ionic dispersion of a polyurethane and the impregnant is coagulated therein.
Another method of forming impregnated porous substrates, and particularly non-woven sheet materials, is described in U.S. Pat. No. 4,376,148 by John McCartney entitled "Impregnated Non-Woven Sheet Material With Ionically Solubilized Resin," incorporated herein by reference. In that patent, needled fibrous batts are impregnated by fully saturating the batt with an aqueous dispersion or emulsion of a polymeric resin. The fully saturated needled batt is contacted with a coagulating agent to coagulate the polymeric resin from the aqueous dispersion and deposit the polymeric resin within the needled batt. The batt is dried to form an impregnated fibrous web having polymeric resin distributed throughout the batt with a density of the web being uniform throughout, and the bulk density of the web being less than the actual density of the web. The impregnated web is characterized by having filaments which are both coated and uncoated with polymeric resin and concentrations of polymeric resin.
A particular utility for the sheet material disclosed in U.S. Pat. No. 4,376,148 is the formation of leather-like materials therefrom. Such processes and compositions are more fully disclosed in U.S. Pat. No. 4,342,805 by John McCartney entitled "Simulated Leather Sheet Material," incorporated herein by reference. In the process of that patent, the impregnated fibrous mass is heated under heat and pressure with the heat and pressure being applied to at least one surface thereof to develop a grain layer on one surface and a split layer on the opposing surface, thus forming the leather-like sheet material. In both of the cited patents, along with U.S. Pat. No. 4,171,391, the preferred polymers are polyurethanes due to their high performance physical and chemical properties. The present invention is an improvement over these impregnation methods in that it utilizes additional polymers as impregnation compositions. These additional polymers provide enhanced properties and also allow for variations in properties for particular end uses.